The present invention relates to a laser survey instrument, by which it is possible to provide a measurement reference plane by a laser beam, and in particular to provide, in addition to a horizontal reference plane, an arbitrary tilt setting plane tilted at a given angle to the horizontal reference plane.
Laser survey instruments are used for providing a horizontal reference plane in wide range instead of optical level.
By such laser survey instruments, the horizontal reference line is formed by projecting a laser beam in a horizontal direction, or the horizontal reference plane is formed by projecting the laser beam in a horizontal direction via a rotating prism.
In architectural engineering work and civil engineering work, positioning and horizontal level setting are performed by utilizing the horizontal reference plane. For example, a reference position is determined by the detection of the laser beam by a photodetector, and this is used for setting-out of mounting position for windows or of a horizontal line for ceiling in interior finishing work.
Also, as proposed by the present applicant in Japanese Patent Publication Laid-Open No. 6-26861, such a laser survey instrument is now used not only for the setting of horizontal level but also in the setting of tilt level, and it is widely used in construction work such as the setting of water drainage inclination of a road or the setting of a road surface gradient.
Description is now given on the laser survey instrument proposed in Japanese Patent Publication Laid-Open No. 6-26861, referring to FIGS. 28 to 35.
At the center of a casing 5, a recess 6 in truncated conical shape is formed, and a support seat 7 is provided at the center of the recess 6. The support seat 7 comprises projections 9, which are protruded smoothly with tertiary curved surface at 3 equally spaced positions on inner periphery of a circular through-hole 8.
A laser projector 10 for emitting a laser beam is placed in the through-hole 8, and a head 11 of the laser projector 10 is engaged in and supported by the support seat 7. The head 11 has its lower portion designed in spherical shape, and this spherical portion 11a slidably contacts the above three projections 9. The laser projector 10 is supported in such manner that it can be tilted in any direction with respect to the vertical line.
A motor seat 14 is provided on the head 11, and a scanning motor 15 is arranged on the motor seat 14. A gear 16 is engaged with the output shaft of a scanning motor 15. The gear 16 is engaged with a scanning gear 17, which is to be described later.
The axis of the laser projector 10 is aligned with the head 11 of the laser projector 10, and a mirror holder 13 is rotatably arranged via a bearing 12. The scanning gear 17 is engaged on the mirror holder 13. As described above, the scanning gear 17 is engaged with the gear 16 so that the mirror holder 13 can be rotated around the vertical shaft by the scanning motor 15. A pentagonal prism 18 is provided on the mirror holder 13, and the laser beam emitted from the laser projector 10 is irradiated in a horizontal direction via a light projecting window 19.
At the middle portion of the laser projector 10, a sensor support shelf 63 is arranged, on which fixed bubble tubes 20 and 21, serving as tilting detectors for detecting the horizontality, are provided so that they are directed perpendicular to each other. The fixed bubble tubes 20 and 21 are electric bubble tubes of capacitance detection type and each of them issues an electrical signal corresponding to a tilt angle with respect to the horizontal plane.
At the lower end of the laser projector 10, a base plate 64 of approximately in form of a right-angled triangle is fixed, and a strut 70 is erected near the vertex of the rectangular portion of the base plate 64, and a ball 67 is fixed on the upper end of the strut 70. An L-shaped tilting plate 62 is arranged above the base plate 64, and a conical recess 99 is formed at the vertex on the rear surface of the tilting plate 62. The ball 67 is engaged with the recess 99, and the apical portion of the tilting plate 62 is supported on the strut 70 so that the tilting plate 62 is pivotable on the ball 67. Further, a spring 68 is provided between the tilting plate 62 and the base plate 64, and the conical recess 99 is pressed against the ball 67, and the tilting plate 62 is pushed clockwise in FIG. 28.
Arbitrary angle setting bubble tubes 65 and 66, serving as tilting movement detectors, are arranged on the tilting plate 62 along the L-shaped portion so that the arbitrary angle setting bubble tubes lie in two directions perpendicular to each other.
A bearing plate 72 is positioned under the sensor support shelf 63 and is protruded from the laser projector 10. Tilting screws 52 and 53 are rotatably mounted at such positions on the base plate 64 as to form a triangle with the strut 70 at its vertex, and the upper ends of the tilting screws 52 and 53 are rotatably supported on the bearing plate 72.
The lower end of the tilting screw 52 is protruded downward from the base plate 64, and tilting gear 54 is engaged with the protruding end of the tilting screw 52. The tilting gear 54 is then engaged with a tilting gear 56 to be described below. The lower end of the tilting screw 53 is protruded downward from the base plate 64, and a tilting gear 55 is engaged with the protruding end of the tilting screw 53. The tilting gear 55 is then engaged with a tilting gear 57 to be described below.
A tilting nut 48 is engaged on the tilting screw 52, and a nut pin 50 having circular cross-section is protruded on the tilting nut 48. A tilting pin 60 having circular cross-section is protruded at such position on the end surface of the tilting plate 62 closer to the arbitrary angle setting bubble tube 65 as to be in parallel to the center line of the arbitrary angle setting bubble tube 65, and the tilting pin 60 is brought into contact with the nut pin 50. Further, two parallel guide pins 71 are connected and they bridge between the base plate 64 and the bearing plate 72, and the tilting pin 60 is slidably held by the two guide pins 71 in order to restrict rotation of the tilting plate 62 in a horizontal direction and to allow the tilting pin 60 to rotate in a vertical direction and around the shaft of the tilting pin 60.
A tilting nut 49 is engaged on the tilting screw 53, and a nut pin 51 having circular cross-section is protruded at such position on the tilting nut 49. A tilting pin 61 having circular cross-section is protruded at such position on the end surface of the tilting plate 62 closer to the arbitrary angle setting bubble tube 66 as to be in parallel to the center line of the arbitrary angle setting bubble tube 66, and the tilting pin 61 is brought into contact with the nut pin 51.
On the lower surface of the base plate 64, a post 73 is suspendedly mounted, and a tilt detecting piece 23, also serving as a motor base, is fixed via this post 73. On the upper surface of the tilt detecting piece 23, tilting motors 58 and 59 are provided, and the tilting gear 56 aforementioned is engaged on the output shaft of the tilting motor 58, and the tilting gear 57 is engaged on the output shaft of the tilting motor 59 so that the tilting gears 56, 57 are engaged with the tilting gears 54 and 55 respectively.
On the lower surface of the tilt detecting piece 23, a ring-shaped reflection mirror is arranged. At positions face-to-face to the tilt detecting piece 23, a given number (4 in the present embodiment) of optical sensors 24a, 24b, 24c and 24d are arranged, each of which comprises a set of light emitting elements and photodetector elements on the same circumferential periphery around the shaft of the laser projector when the casing 5 and the laser projector 10 are positioned perpendicularly to each other.
From the head 11 of the laser projector 10, tilting arms 25 and 26 are extended in horizontal directions and perpendicularly to each other. The tilting arms 25 and 26 are passed through the conical surface of the recess 6 and are positioned inside the casing 5, and engaging pins 27 and 28 are protruded at forward ends of the tilting arms 25 and 26. The engaging pins 27 and 28 are designed in cylindrical shape, and the axes of the cylinders run perpendicularly to each other and are included in a plane, which passes through the center of the spherical portion 11a. One of the engaging pins 27 and 28, e.g. the engaging pin 27, is restricted to move in horizontal direction so that it can be moved only in the vertical direction. Although not shown in the figure, the engaging pin 27 is slidably engaged in a guide groove extending in the vertical direction, or the engaging pin 27 is slidably pressed against the wall surface extending in the vertical direction by a resilient means such as a spring.
Shelf plates 29 and 30 are provided on inner wall of the casing 5. A level adjusting motor 31 is arranged on the shelf plate 29, and a level adjusting motor 32 is arranged on the shelf plate 30. A driving gear 33 is engaged on the pivot shaft of the level adjusting motor 31, and the driving gear 34 is engaged on the level adjusting motor 32. A screw shaft 35 running perpendicularly to the engaging pin 27 and bridging over the ceiling of the casing 5 and the shelf plate 29 is rotatably arranged. A driven gear 36 is engaged on the screw shaft 35, and the driven gear 36 is also engaged with the driving gear 33. A slide nut 37 is engaged with the screw shaft 35, and a pin 38 is protruded on the slide nut 37, and the pin 38 is slidably brought into contact with the engaging pin 27.
Similarly, a screw shaft 39 running perpendicularly to the engaging pin 28 and bridging over the ceiling of the casing 5 and the shelf plate 30 is rotatably arranged. A driven gear 40 is engaged with the screw shaft 39, and the driven gear 40 is also engaged with the driving gear 34. A slide nut 41 is engaged with the screw shaft 39, and a pin 42 is protruded on the slide nut 41, and the pin 42 is slidably brought into contact with the engaging pin 28.
A spring receptacle 43 is provided between the ceiling of the casing 5 and the screw shaft 35 or the screw shaft 39, and a spring 44 is placed between the spring receptacle 43 and the laser projector 10 so that the laser projector 10 is pushed clockwise around the support seat 7 in FIG. 28.
In the figure, reference numeral 45 represents a battery box to accommodate a battery for driving the laser survey instrument. The main unit 4 of the laser survey instrument is mounted on a tripod (not shown) via leveling bolts 46 for leveling. Reference numeral 47 represents a glass window encircling the mirror holder 13.
FIG. 33 is a block diagram for a control unit of the above conventional type instrument.
Detection results of the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 are inputted to an angle detection circuit 87 via a switching circuit 85, and detection results of the fixed bubble tube 21 and the arbitrary angle setting bubble tube 66 are inputted to an angle detection circuit 88 via a switching circuit 86. On the angle detection circuits 88 and 87, reference angles 92 and 91 are set respectively. The reference angles 91 and 92 are usually 0.degree. respectively.
When a signal from the fixed bubble tube 20 is inputted to the angle detection circuit 87 by the switching circuit 85, the angle detection circuit 87 detects a deviation from the reference angle 91, and the signal of the angle detection circuit 87 is inputted to a motor controller 89. Then, the level adjusting motor 31 is driven and controlled by the motor controller 89.
When signals from the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 are inputted to the angle detection circuit 87 by the switching circuit 85, the angle detection circuit 87 issues a signal corresponding to the deviation. This signal is inputted to a tilt driving circuit 83, and the tilting motor 58 is driven and controlled by the tilt driving circuit 83. When a signal from the arbitrary angle setting bubble tube 65 is inputted to the angle detection circuit 87 by the switching circuit 85, the angle detection circuit 87 detects the deviation from the reference angle 91, and the signal of the angle detection circuit 87 is inputted to the motor controller 89. Then, the level adjusting motor 31 is driven and controlled by the motor controller 89.
The signal of the angle detection circuit 88 is inputted to a motor controller 90, and the level adjusting motor 32 is driven and controlled by the motor controller 90. A signal from the angle detection circuit 88 and a signal from an arbitrary angle setter 82 are inputted to a tilt driving circuit 84, and the tilting motor 59 is driven and controlled by the tilt driving circuit 84.
The angular deviations of the angle detection circuits 87 and 88 are inputted to a discriminator 93. The discriminator 93 selects a higher angular deviation from the angular deviations of the angle detection circuits 87 and 88 and issues an output corresponding to the selected angular deviation change to a display unit driver 94, which displays a value corresponding to the deviation on a display unit 95.
A reference plane formed by laser beam can be set in horizontal direction or at any angle. In the following, description will be given on the leveling operation of the laser survey instrument to form the horizontal reference plane.
When the main unit 4 is installed and no adjustment is made yet, the axis of the laser projector 10 is generally not aligned with the vertical line, and the fixed bubble tubes 20 and 21 are not in horizontal position. The switching circuits 85 and 86 operate in such manner that the signals from the fixed bubble tubes 20 and 21 are inputted to the angle detection circuits 87 and 88.
If it is assumed that the reference angles 91 and 92 are 0.degree. respectively, angular deviation signals are outputted from the angle detection circuits 87 and 88. When the angular deviation signals are outputted, the motor controllers 89 and 90 drive the level adjusting motors 31 and 32 in a given direction so that the angular deviation signals are turned to 0.
The operation relating to the level adjusting motors 31 and 32 is now described, taking an example in the case of the level adjusting motor 31.
When the level adjusting motor 31 is driven, rotation of the level adjusting motor 31 is transmitted to the screw shaft 35 via the driving gear 33 and the driven gear 36, and the slide nut 37 is moved up or down by rotating the screw shaft 35. The upward or downward movement of the slide nut 37 is transmitted to the tilting arm 25 via the pin 38 and the engaging pin 27, and the laser projector 10 is tilted.
As described above, the movement of the engaging pin 27 is restricted in horizontal direction and it is allowed to move only in vertical direction. Thus, tilting direction of the laser projector 10 is restricted and it is tilted around the axis of the engaging pin 28, which runs through the center of the spherical portion 11a. Next, when the level adjusting motor 32 is driven, the screw shaft 39 is rotated, and the engaging pin 28 is moved up or down via the pin 42.
Because the horizontal movement of the engaging pin 27 is restricted by a groove (not shown) and its vertical movement is restricted by the pin 38 and the spring 44, the engaging pin 27 is allowed only to rotate around the axis of the engaging pin 27, which runs through the center of the spherical portion 11a.
When the pin 42 is moved up or down, a change in vertical movement is given to the engaging pin 28 with sliding movement in axial direction between the pin 42 and the engaging pin 28, and the laser projector 10 is tilted around the axis of the engaging pin 27. As described above, the cross-section of the engaging pin 27 is circular. Thus, the tilting of the axis of the engaging pin 27 is not changed when the engaging pin 27 is rotated. That is, tilting by the level adjusting motors 31 and 32 give no influence on the other tilting axes, i.e. the tilting of the axes of the engaging pins 27 and 28. Therefore, tilting adjustment of one axis can be performed independently from the tilting adjustment of the other axis, and the operation of tilting adjustment and control sequence relating to the operation of the tilting adjustment can be extensively simplified.
Because the laser projector 10 is pushed clockwise in FIG. 28 by the spring 44, the laser projector 10 accurately follows the movement of the slide nut 37.
In the tilting operation of the laser projector 10, the support of the laser projector 10 is stable because the spherical portion 11a of the laser projector 10 is supported at three points via the projections 9. Because it is the contact between the spherical portion 11a and the projections 9 having smooth curved surfaces, the laser projector 10 is smoothly moved in any tilting direction, and the posture of the laser projector 10 can be easily adjusted and controlled.
When the laser projector 10 is tilted and leveling operation proceeds, the detection values from the fixed bubble tubes 20 and 21 are brought closer to horizontal. Finally, angular deviations issued from the motor controllers 89 and 90 are turned to 0, and leveling operation is completed.
Detection range of the fixed bubble tubes 20 and 21 is narrow, and saturation status occurs when it exceeds the predetermined range. Thus, tilting direction can be detected, but the value of the tilting angle cannot be detected. Therefore, the optical sensors 24a, 24b, 24c and 24d are provided so that the adjusting mechanism, comprising the level adjusting motors 31 and 32, the driving gears 33 and 34, the driven gears 36 and 40, the screw shafts 35 and 39, the slide nuts 37 and 41, and the tilting arms 25 and 26, is not moved beyond the mechanical adjusting range. Namely, when the limit of the mechanical adjusting range is reached, the light emitted from one of the optical sensors 24a, 24b, 24c and 24d is reflected by the reflection mirror arranged on the tilt detecting piece 23 and is detected by the optical sensor. As a result, the reaching at the limit of the mechanical adjusting range is detected, and the level adjusting motors 31 and 32 are stopped, or it is displayed on the display unit or a buzzer alarm is issued.
In such case, rough adjustment is made to fall in the adjusting range by utilizing the leveling bolts 46, and leveling operation will be started again.
When the leveling operation is completed, laser beam is emitted from the laser projector 10. Further, the scanning motor 15 is driven to rotate the laser projector 10 around the vertical axis, and laser beam is irradiated in horizontal direction through the pentagonal prism 18. By rotating it further, a horizontal reference plane is formed by the laser beam.
In the process of the leveling operation, some time is required from the starting to the completion of leveling. During this period, the progress of the leveling operation is displayed for the operator to inform that the leveling operation is being performed adequately and to eliminate the sense of uneasiness of the operator.
The magnitude of angular deviation issued from the angle detection circuits 87 and 88 is judged by the discriminator 93, and higher angular deviation is selected. The change of the selected angular deviation is outputted to the display unit driver 94, and the content of the display is altered according to the change of the angular deviation. Then, it is displayed on the display unit 95.
The higher angular deviation is selected because more time is required for angular adjustment of higher angular deviation. Instead of selecting magnitude of angular deviation, the sum of the angular deviations outputted from the angle detection circuits 87 and 88 may be obtained and the content of the display may be changed according to the sum of the angular deviations.
FIG. 34 is a diagram showing relationship between angular deviation and time. Based on this relationship, a position to change the display content is set in advance. When the angular deviation reaches the preset position, the display is switched over, and the progress of the leveling operation is notified to the operator.
Next, description is given on the case where the reference plane formed by the laser beam is set at an arbitrary angle after the horizontal reference plane is formed as described above.
The numerical values to tilt the reference plane by the arbitrary angle setters 81 and 82 are inputted to the tilt driving circuits 83 and 84 respectively.
It is determined whether or not the detection results of the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 are identical with those of the fixed bubble tube 21 and the arbitrary angle setting bubble tube 66, and these are made identical with each other. In this case, it is preferable that the fixed bubble tubes 20 and 21 are in horizontal position, whereas these may not be in horizontal position and it will suffice if these are not in saturation status.
When the outputs from the fixed bubble tubes 20 and 21 and the arbitrary angle setting bubble tubes 65 and 66 are identical with each other, the arbitrary angle setting bubble tubes 65 and 66 are tilted at the angles as set by the arbitrary angle setters 81 and 82, and the laser projector 10 is tilted so that the arbitrary angle setting bubble tubes 65 and 66 are turned to horizontal position. Then, the rotation axis of the laser projector 10 for forming an arbitrary angle reference plane can be obtained. Thus, when the laser projector 10 is rotated to form a reference plane, the laser beam reference plane is formed as desired.
Further, more concrete description will be given below. Because the angle setting operation for the arbitrary angle setting bubble tube 65 is similar to the angle setting operation for the arbitrary angle setting bubble tube 66, description will be given below only for the arbitrary angle setting bubble tube 65.
A switching signal is inputted to the switching circuit 85 from an input unit or a control unit (not shown), and a signal from the fixed bubble tube 20 and a signal from the arbitrary angle setting bubble tube 65 are inputted to the angle detection circuit 87. In case deviation of angles detected by the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 is obtained in the angle detection circuit 87, and if a deviation is present, this deviation signal is inputted to the tilt driving circuit 83.
The tilt driving circuit 83 drives the tilting motor 58. When the tilting motor 58 is driven, the tilting gear 56 is rotated, and the rotation of the tilting gear 56 is transmitted to the tilting screw 52 via the tilting gear 54, and the tilting nut 48 is moved up or down in a given direction. When the nut pin 50 of the tilting nut 48 is engaged with the tilting pin 60, the tilting plate 62 is tilted in such a direction that the deviation is turned to 0.
The tilting of the tilting plate 62 is detected by the arbitrary angle setting bubble tube 65 and is further inputted to the angle detection circuit 87 via the switching circuit 85.
By the angle detection circuit 87, deviation of the detected angles of the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 is sequentially calculated, and the detected angular deviation is fed back to the tilt driving circuit 83, and the tilting motor 58 is driven until the detected angular deviation is turned to 0.
When the detected angular deviation is 0, the axis of the laser projector 10 runs perpendicularly to the plane detected by the arbitrary angle setting bubble tubes 65 and 66.
Next, the preset angle is inputted to the tilt driving circuit 83 by the arbitrary angle setter 81, and the tilting reference plane setting operation is started.
In the tilt driving circuit 83, the tilting motor 58 is driven so that the angle corresponding to the preset angle inputted by the arbitrary angle setter 81 is reached, and the tilting plate 62 is tilted in a direction reverse to the tilting reference plane to be obtained.
Here, for example, a pulse motor is used as the tilting motor 58, and the tilting angle of the tilting plate 62 and the number of pulses of the pulse motor required for the tilting are stored in the tilt driving circuit 83 in advance. Then, the number of pulses corresponding to the angle set by the arbitrary angle setter 81 is outputted to drive the tilting motor 58.
The tilting screw 52 is rotated by the tilting motor 58, and the tilting nut 48 is moved in a given direction, e.g. in downward direction.
The movement of the tilting nut 48 is transmitted to the tilting plate 62 via the nut pin 50 and the tilting pin 60 as described above, and the tilting plate 62 is tilted counterclockwise in FIG. 28 around the ball 67.
As already described, the tilting pin 60 is guided by the guide pin 71 and is tilted only in vertical direction. Accordingly, the tilting of the tilting pin 60 gives no influence on the tilting of the arbitrary angle setting bubble tube 66.
When the tilting plate 62 is tilted, the output value from the angle detection circuit 87 is changed, and the comparison result calculated by the tilt driving circuit 83 decreases.
When the comparison result is turned to 0, the driving of the tilting motor 58 is stopped, and the tilting setting operation of the tilting plate 62 is completed. The signal of this completion is also inputted to the switching circuit 85, and the circuit is switched over in such manner that only the signal from the arbitrary angle setting bubble tube 65 is inputted to the reference angle 91.
The tilting operation relating to the arbitrary angle setting bubble tube 66 is also performed in similar manner. Because the tilting pin 60 is guided by the guide pin 71 as described above, the tilting operation of the arbitrary angle setting bubble tube 66 gives no influence on the arbitrary angle setting bubble tube 65. Therefore, the tilting operations in two directions of the tilting plate 62 can be independently controlled, and control sequence relating to the two-direction tilting operation of the tilting plate 62 is simple.
When the tilting setting operation of the tilting plate 62 is completed, tilting operation of the laser projector 10 is started based on the detection results of the arbitrary angle setting bubble tube 65 in order to set the tilting reference plane. The setting operation of the tilting of the laser projector 10 is performed in such manner that the detection results of the arbitrary angle setting bubble tube 65 are in a horizontal direction. Because this operation is similar to the case where leveling operation is performed based on the fixed bubble tubes 20 and 21, detailed description is not given here.
FIG. 32 represents the status where the setting operation of the tilting reference plane has been completed. When the setting operation of the tilting reference plane is completed, the tilting plate 62 is in horizontal position.
The concurrent operation of the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 is carried out to guarantee the accuracy of the tilting operation of the tilting plate 62. This may be performed each time the tilting operation is carried out or after it has been repeated by the predetermined times.
FIG. 35 represents an example of a controller 96 incorporated with the arbitrary angle setters 81 and 82. The tilting of the tilting plate 62 is supported by the tilting of two axes (X and Y), and the preset numerical values are displayed on the display units 97 and 98.
In the above, it is described that adjustment has been already completed as to in which direction the reference plane formed by laser beam should be tilted. In fact, accurate setting must be made first in a desired direction (horizontal direction), in which the main unit 4 of the laser survey instrument should be tilted.
In the past, to perform the setting operation to set the main unit in a direction to be tilted, a collimator 75 arranged on the upper surface of the main unit 4 as shown in FIG. 28 has been used. Tilting direction of the tilt setting mechanism in the main unit is set in parallel to longitudinal direction of the bubble tube, which sets and detects the tilting, and mechanical arrangement is made in such manner that collimating direction of the collimator 75 is also in parallel to the tilt setting mechanism. The direction of the main unit is also aligned with the tilt setting mechanism. The operation to set the collimator 75 in a direction to be tilted is to rotate or move the main unit and to turn the tilting direction of the tilt setting mechanism in the main unit and the bubble tube toward the predetermined direction. In the meantime, the main unit is usually mounted on a tripod, and description will be given now on the operation on the tripod.
A target (not shown) is installed in advance in a direction, in which the tilting should be set, and by directing the main unit of the laser survey instrument in a direction accurately facing to the target using the collimator 75, main unit 4 can be set in the direction, in which it is to be tilted.
The screws (not shown) fixing the main unit 4 are loosened, and the main unit 4 is rotated. The target is collimated from the collimator 75, and the direction of the main unit 4 is accurately set toward the target.
As it is evident from the above description, the horizontal line is used as reference in the setting of an internal tilt angle (an angle of elevation) in a series of setting operations for the laser survey instrument, and it is performed according to tilting information electrically detected by a tilt detector such as bubble tube. Thus, there will be no man-made error by the surveyor. As a result, tilt angle can be set at high accuracy.
On the other hand, in the operation to set the main unit 4 in a direction to be tilted, the collimator 75 is used, and it is up to personal judgment of the surveyor to decide whether it is aligned or not. Further, the collimator 75 requires no high technical skill to collimate, and unlike a collimating telescope, collimating accuracy is not high. For this reason, the setting by means of the collimator 75 does not give high accuracy in the setting of the direction because of low accuracy of the collimator 75 itself and of the man-made error.
In conventional type civil engineering work, which does not necessarily require high accuracy, there has been no special problem in the direction setting using the collimator 75, whereas, in the highly mechanized civil engineering work in recent years, the problem of accuracy arises.